This invention relates generally to keyswitches for use in keyboards and more particularly to a keyswitch having a novel internal construction which provides superior alignment and stability of the key tops of such switches.
In the past, various types of keyboards have been used on typewriters, computer terminals and the like for typing or entering data into a computer. Such keyboards are typically manufactured from a plurality of separate keyswitches which are lined up on a circuit board. Each individual keyswitch has a key top thereon which is generally stamped or otherwise marked with the number or letter which that keyswitch represents. Thus, a keyboard for a conventional typewriter will have something on the order of 50 separate keyswitches, 26 of them representing the letters of the alphabet, 10 representing the digits 0-9, with additional switches for various punctuation and machine functions.
Keyswitches of conventional design generally include a plunger which is slidably mounted within a housing. The plunger is designed to slide downwardly when the key top of the keyswitch is pressed. Downward pressure on the key top actuates an electrical switch coupled to the plunger. Due to clearance between the switch housing and the plunger in keyswitches of conventional design, the key tops exhibit excessive movement in directions perpendicular to the desired downward direction of movement. Such movement results in noise, if the keyboard is shaken, and in undesirable lateral motion of the key tops. The same clearance conditions also enable the keytops to be rotated by varying amounts about the longitudinal axis of the plunger. This movement is undesirable because it results in a staggered or non-aligned condition of the key tops when viewed as a group, causing a poor cosmetic appearance of the keyboard assembly. Such rotational movement also contributes to the keyboard noise.
The above-mentioned undesirable characteristics of prior art keyboards result, in large part, from inherent tolerence variations of the plastic components (e.g. plunger, housing etc.) from which the keyswitches are manufactured. Variations in mold and die dimensions, as well as plastic material formulations and temperature parameters all contribute to such tolerance variations.
It would be advantageous to provide a keyswitch that is self aligning when in its normal, non-depressed state. Such a keyswitch should be easy to manufacture, economical, and provide a uniform appearance when a plurality of such switches are used to construct a complete keyboard. Further, such a switch should minimize lateral movement of the plunger in the switch housing, thereby reducing any keyswitch noise to a minimum. The present invention relates to such a keyswitch.